This invention relates to a dielectric ceramic composition for high frequencies. More particularly, the invention relates to a dielectric ceramic composition for microwave devices designed to operate at frequencies of 300 MHz to 30 GHz, having high permittivity and high Q and being stable in temperature characteristics.
Recently, it has been attempted to miniaturize microwave circuits with the advance of technology in high frequency circuits designed to operate at microwave and millimeter wave frequencies having a wave length of not more than several ten centimeters.
In such high frequency circuits, there have been used cavity resonators and antennas. However, such conventional elements must have the sizes corresponding to the wave lengths of microwaves so that the use of such elements is an obstacle to miniaturize the circuits. In order to overcome such a disadvantage, it has been proposed to use dielectric ceramic materials in place of conventional metal materials. Many of the dielectric ceramic materials commonly used consist essentially of compositions of the titanate system, such as CaTiO.sub.3 -MgTiO.sub.3 -La.sub.2 O.sub.3.sup.. 2TiO.sub.2 or MgTiO.sub.3 -CaTiO.sub.3. It is, however, impossible with such compositions to produce dielectric elements having adequate characteristics required for the application to the microwave devices. Although the dielectric materials are required to have low dielectric loss, high permittivity and small temperature coefficient of permittivity, none of said compositions have sufficient characteristics which satisfy the above requirements, simultaneously.
It is therefore an object of the present invention to provide a dielectric ceramic composition for high frequencies having high permittivity and high Q (i.e., low dielectric loss).
Another object of the present invention is to provide a dielectric ceramic composition for high frequencies having small temperature coefficient of resonant frequency.
A further object of the present invention is to provide a dielectric ceramic composition for high frequencies which makes it possible to obtain dielectric ceramic elements having an optional temperature coefficient of resonant frequency in the range of from - 20 .times. 10.sup.-6 /.degree. C. to + 56 .times. 10.sup.-6 /.degree. C. by the variation of the compositional proportions.
According to the present invention, there is provided a dielectric ceramic composition for high frequencies consisting essentially of 83 to 99.8 wt% of a basic composition composed of 22 to 43 wt% of titanium dioxide (TiO.sub.2), 38 to 58 wt% of zirconium dioxide (ZrO.sub.2) and 9 to 26 wt% of stannic oxide (SnO.sub.2), and 0.2 to 17 wt% of one or two additive selected from the group consisting of lanthanum oxide (La.sub.2 O.sub.3), cobaltic oxide (Co.sub.2 O.sub.3) and zinc oxide (ZnO).
When lanthanum oxide is used alone as the additive, the content thereof is preferably from 0.5 to 10 wt%. However, when lanthanum oxide is used together with zinc oxide as the additive, the content thereof is preferably not more than 2 wt%. When cobaltic oxide is used alone or together with zinc oxide as the additive, the content thereof is preferably not more than 10 wt%. When zinc oxide is used alone or together with lanthanum oxide or cobaltic oxide as the additive, the content thereof is preferably not more than 7 wt%. However, when zinc oxide is used alone, the content thereof is preferably not less than 1.2 wt%.
The above-mentioned limitation on the proportion of the constituents is required for the following reasons.
If titanium dioxide is less than 22 wt%, the permittivity of the products becomes small while on the other hand larger amount than 43 wt% causes the great increase of the temperature coefficient of resonant frequency. If zirconium dioxide is present in an amount less than 38 wt% or more than 58 wt%, the temperature coefficient of resonant frequency becomes too large. If stannic oxide is present in an amount smaller than 9 wt%, Q becomes small, and larger amount than 26 wt% causes the increase of the temperature coefficient of resonant frequency.
In cases where lanthanum oxide is used alone as the additive, if lanthanum oxide present is smaller than 0.5 wt%, the sintering of the product becomes insufficient, resulting in the deterioration of the permittivity and Q while on the other hand larger amount than 10 wt% causes the deterioration of Q. In cases where lanthanum oxide is used together with zinc oxide as the additive, if lanthanum oxide present is larger than 2 wt%, it causes the deterioration of Q.
In cases where cobaltic oxide is used alone or together with zinc oxide as the additive, if cobaltic oxide present is larger than 10 wt%, it causes the deterioration of the permittivity and Q. In cases where cobaltic oxide is used alone, if cobaltic oxide present is samller than 0.2 wt%, it is impossible to obtain a sufficiently sintered ceramic body.
In cases where zinc oxide is used alone or together with lanthanum oxide or cobaltic oxide as the additive, if zinc oxide present is larger than 7 wt%, it causes the deterioration of the permittivity and Q. In cases where zinc oxide is used alone, if zinc oxide present is smaller than 1.2 wt%, it is impossible to obtain a sufficiently sintered ceramic body.
The dielectric ceramic compositions of the present invention may be prepared by technique conventionally employed for the production of dielectric ceramic compositions. A preferred method, however, hereinafter described, consists in the use of highly purified oxides.
The highly purified oxides, viz, TiO.sub.2, ZrO.sub.2, SnO.sub.2, La.sub.2 O.sub.3, ZnO are used as starting materials for the preparation of the dielectric ceramic materials of the examples shown in Tables 1 and 2. In each example, the mixture of powdered starting materials having the compositional proportion shown in Tables 1 and 2 was ball milled with water for 16 hours, then the resulting mixture was dehydrated, dried and molded into a disk having a diameter of 12 mm and a thickness of 5.5 mm under a pressure of 2500 kg/cm.sup.2. The disk was sintered in natural atmosphere at 1320.degree. C. for 4 hours to convert it to a dielectric ceramic body.
The measurements of the electrical properties were made for each ceramic body of the examples. The results obtained are shown in Tables 1 and 2. The properties given in the tables are the permittivity, Q and temperature coefficient of resonant frequency at a microwave frequency of 7 GHz and at 25.degree. C. In the tables, the asterisks (*) designate compositions beyond the scope of the present invention.
The permittivity and Q at microwave frequency were measured by the well-known dielectric resonant method. The temperature coefficient of resonant frequency, TC(fo), represents the change rate of the resonant frequency (fo) over the temperature range of from +25.degree. to +85.degree. C. The change rate of resonant frequency, TC(fo), on temperature was derived from the temperature coefficient of permittivity, TC(.epsilon.), and the temperature coefficient of expansion, .alpha., of the ceramic body. Thus, the relationship between the temperature coefficient of resonant frequency, TC(fo), and the temperature coefficient of permittivity, TC(.epsilon.), is given by the equation: EQU TC(fo)=- 1/2 TC(.epsilon.) - .alpha.
it will be seen from the results shown in Tables 1 and 2 that according to the present invention it is possible to obtain dielectric ceramic compositions having high permittivity in the range of 29.3 to 44.2 and high Q in the range of 4100 to 9500 at microwave frequencies and at 25.degree. C. In addition, the dielectric ceramic compositions of the present invention have small temperature coefficients of resonant frequency. Furthermore, according to the present invention it is possible to prepare a dielectric ceramic composition having an optional temperature coefficient of resonant frequency in the range of from - 20 .times. 10.sup.-6 /.degree. C. to + 56 .times. 10.sup.-6 /.degree. C. by the variation of the compositional proportions, thus making it possible to provide dielectric ceramic elements with the temperature compensating function for the other electrical elements in the high frequency circuits in which said ceramic elements are incorporated. Thus, the dielectric ceramic compositions according to the invention are suitable for use as dielectric resonators in microwave bandpass filters, or as antennas employed at microwave frequencies, or as substrates for microwave circuits.
Table 1 __________________________________________________________________________ Basic Additive composition (wt %) (wt %) TC Ex. TiO.sub.2 ZrO.sub.2 SnO.sub.2 La.sub.2 O.sub.3 .epsilon. Q (.times. 10.sup.-6 /.degree. C.) __________________________________________________________________________ 1* 20 56 24 4.0 32.7 5800 -10 2 22 52 26 " 32.9 5700 -12 3 22 58 20 " 33.0 6000 +39 4 24 52 24 " 33.4 6500 - 8 5 24 56 20 " 33.5 5900 + 2 6 28 48 24 " 33.5 6000 - 9 7 28 52 20 " 34.2 6600 - 4 8 28 56 16 " 34.7 5300 +22 9 32 44 24 " 34.5 6800 -16 10 32 48 20 " 34.6 6800 - 4 11 32 52 16 " 35.6 5100 + 1 12 32 56 12 " 36.7 4700 +25 13 33 58 9 " 37.8 4100 +36 14 36 38 26 " 35.6 6000 + 4 15 36 44 20 " 36.2 6800 - 7 16 36 48 16 " 36.9 6100 - 1 17 36 52 12 " 37.8 4900 +11 18* 40 36 24 " 42.2 6200 +76 19 40 40 20 " 39.6 6000 +24 20 40 44 16 " 39.0 6000 + 4 21 40 48 12 " 39.0 5000 + 9 22 43 38 19 " 39.2 5700 +56 23 43 48 9 " 42.1 4900 +24 24* 46 42 12 " 45.6 5000 +76 25 22 52 26 0.5 29.3 3500 26 " " " 1 33.1 5200 27 " " " 4 32.9 5700 -12.+-.5 28 " " " 10 32.9 4900 29* " " " 20 32.8 2500 30 32 52 16 0.5 32.4 3000 31 " " " 4 35.6 5100 + 1.+-.5 32 " " " 10 35.5 4300 33* " " " 20 35.5 2000 34 36 38 26 0.5 31.8 4000 35 " " " 1 35.7 5400 36 " " " 4 35.6 6000 + 4.+-.5 37 " " " 10 35.6 4200 38* " " " 20 35.6 2900 39 40 48 12 0.5 36.1 3100 40 " " " 1 39.1 4400 41 " " " 4 39.0 5000 + 9.+-.5 42 " " " 10 39.0 4200 43* " " " 20 38.9 2000 44* 20 56 24 0.5 33.6 8200 -10 45 22 52 26 " 33.7 9000 -11 46 22 58 20 " 33.8 8400 +40 47 24 52 24 " 34.0 8900 - 9 48 24 56 20 " 34.2 8400 0 49 28 48 24 " 34.5 8300 -10 50 28 52 20 " 35.0 9000 - 5 51 28 56 16 " 35.5 7800 +20 52 32 44 24 " 35.3 9200 -15 53 32 48 20 " 35.5 9500 - 5 54 32 52 16 " 36.3 8400 + 1 55 32 56 12 " 37.4 7100 +21 56 33 58 9 " 38.6 6500 +35 57 36 38 26 " 36.5 8600 + 4 58 36 44 20 " 37.0 9200 - 8 59 36 48 16 " 37.7 8500 - 1 60 36 52 12 " 38.6 7400 +10 61* 40 36 24 " 43.1 8600 +75 62 40 40 20 " 40.4 8600 +20 63 40 44 16 " 39.7 8400 + 4 64 40 48 12 " 39.9 7500 + 8 65 43 38 19 " 44.0 8100 +51 66 43 48 9 " 42.9 7400 +23 67* 46 42 12 " 46.3 7600 +73 68 22 52 26 0.2 33.4 8200 69 " " " 0.5 33.7 9000 70 " " " 1 33.0 8800 71 " " " 3 31.5 7600 -11.+-.7 72 " " " 5 30.9 7200 73 " " " 10 29.5 6000 74* " " " 20 28.4 4200 75 32 52 16 0.5 36.3 8400 76 " " " 1 35.7 7600 +1.+-.7 77 " " " 10 32.1 5500 78* " " " 20 31.0 4100 79 36 38 26 0.2 36.4 8000 80 " " " 0.5 36.5 8600 81 " " " 1 35.9 8300 +4.+-.7 82 " " " 3 34.5 7200 83 " " " 10 32.2 5800 84* " " " 20 31.1 4100 85 40 48 12 0.5 39.9 7500 86 " " " 1 39.2 6600 +8.+-.7 87 " " " 5 36.9 5500 88* " " " 20 34.4 3400 89* 28 58 14 1.5 35.0 5100 +32 90 30 46 24 " 33.0 7600 -20 91 30 30 12 " 36.0 4800 +37 92 31 51 18 " 34.3 6100 - 1 93 31 54 15 " 35.4 5900 +13 94* 32 42 26 " 33.0 7500 -52 95 33 58 9 " 37.5 4500 +38 96 34 45 21 " 35.0 7800 -10 97 34 48 18 " 35.5 7400 - 3 98 34 51 15 " 36.1 6400 + 1 99 34 54 12 " 37.5 5400 +12 100 36 40 24 " 35.0 7000 -33 101 37 42 21 " 36.2 7000 - 9 102 37 45 18 " 36.6 7400 - 7 103 37 48 15 " 37.7 6300 + 1 104 37 51 12 " 37.7 5500 + 8 105 40 42 18 " 39.0 7000 + 7 106 40 45 15 " 38.5 6300 + 4 107 40 48 12 " 38.9 5900 + 5 108 43 40 17 " 42.5 6500 +32 109 43 48 9 " 41.9 5600 +23 110* 46 42 12 " 46.6 6000 +75 __________________________________________________________________________
Table 2 __________________________________________________________________________ Basic Additive composition (wt %) (wt %) TC Example TiO.sub.2 ZrO.sub.2 SnO.sub.2 ZnO La.sub.2 O.sub.3 .epsilon. Q (.times. 10.sup.-6 /.degree. C.) __________________________________________________________________________ 111* 20 56 24 1.0 0.5 33.8 6500 - 9 112 22 52 26 " " 33.9 6400 -12 113 22 58 20 " " 33.9 6700 +43 114 24 52 24 " " 34.2 7300 - 9 115 24 56 20 " " 34.4 6500 0 116 28 48 24 " " 34.7 6800 -11 117 28 52 20 " " 35.2 7200 - 5 118 28 56 16 " " 35.7 5900 +21 119 32 44 24 " " 35.6 7400 -16 120 32 48 20 " " 35.7 7500 - 4 121 32 52 16 " " 36.5 5800 + 1 122 32 56 12 " " 37.5 6400 +20 123 33 58 9 " " 38.8 4800 +38 124 36 38 26 " " 36.7 6900 + 4 125 36 44 20 " " 37.2 7700 - 7 126 36 48 16 " " 37.9 6800 - 1 127 36 52 12 " " 38.8 5500 +12 128* 40 36 24 " " 43.3 6900 +79 129 40 40 20 " " 40.6 6700 +21 130 40 44 16 " " 39.9 6600 + 4 131 40 48 12 " " 40.2 5700 + 7 132 43 38 19 " " 44.2 6400 +55 123 43 48 9 " " 43.1 5700 +25 134* 46 42 12 " " 46.5 5600 +75 135 22 52 26 0.5 0.2 34.3 6800 136 " " " " 1 34.3 5000 137* " " " " 3 34.2 500 138 " " " 1 0.5 33.9 6400 -12.+-.5 139 " " " 3 2 33.0 5000 140 " " " 7 0.2 31.9 4900 141* " " " " 3 31.9 300 142* " " " 10 2 30.7 500 143 32 52 116 0.5 0.2 36.7 6200 144* " " " " 3 36.6 200 145 " " " 1 0.5 36.5 5800 146 " " " " 1 36.4 4900 147 " " " 3 " 35.6 5500 + 1.+-.5 148 " " " " 2 35.5 4300 149* " " " " 3 35.5 300 150 " " " 7 0.2 34.3 4200 151* " " " " 3 34.2 200 152* " " " 10 2 33.1 300 153 36 38 26 0.5 0.5 36.7 6900 154 " " " " 2 36.9 4900 155* " " " " 3 36.8 300 + 4.+-.5 156 " " " 1 2 36.7 4500 157 " " " 7 0.5 34.8 4500 158* " " " " 3 34.6 200 159 43 38 19 0.5 0.2 40.5 6100 160* " " " " 3 40.4 500 161 " " " 1 0.5 40.2 5700 162 " " " 3 1 39.3 5400 + 7.+-.6 163 " " " " 2 39.2 4800 164* " " " 7 3 38.1 200 165* " " " 10 1 36.8 1900 166* 20 56 24 1.5 0.25 32.5 6800 -12 167 22 52 26 " " 32.7 6600 - 8 168 22 58 20 " " 32.8 6900 +39 169 24 52 24 " " 33.1 7500 - 9 170 24 56 20 " " 33.3 6900 - 1 171 28 48 24 " " 33.5 6900 -11 172 28 52 20 " " 34.0 7500 - 4 173 28 56 16 " " 34.6 6200 +21 174 32 44 24 " " 34.3 7700 -16 175 32 48 20 " " 34.5 7800 - 5 176 32 52 16 " " 35.4 6000 0 177 32 56 12 " " 36.5 5600 +23 178 33 58 9 " " 37.6 5100 +36 179 36 38 26 " ` 35.4 7000 + 7 180 36 44 20 " " 36.0 7700 - 9 181 36 48 16 " " 36.7 7000 - 1 182 36 52 12 " " 37.7 5800 + 9 183* 40 36 24 " " 42.0 7100 +78 184 40 40 20 " " 39.4 7000 +18 185 40 44 16 " " 38.8 6900 + 3 186 40 48 12 " " 38.9 5900 + 9 187 43 38 19 " " 39.0 6600 +52 188 43 48 9 " " 42.0 5800 +26 189* 46 42 12 " " 45.4 6000 +78 190 22 52 26 0.5 0.5 32.9 7300 191 " " " " 1 32.6 7600 192 " " " " 10 30.5 6100 193* " " " " 20 29.7 5000 194 " " " 1.5 1 32.3 7100 195 " " " " 3 31.6 7200 196 " " " " 10 30.5 6400 197* " " " " 20 29.9 5500 -8.+-.4 198 " " " 3.0 1 31.6 6500 199 " " " " 3 30.6 6400 200* " " " " 20 28.6 4400 201 " " " 7.0 0.5 30.5 5200 202 " " " " 3 29.3 5000 203* " " " " 20 27.4 3000 204* " " " 10.0 3 28.4 4500 205* " " " " 10 27.2 3600 206 32 " 16 0.5 1 35.4 6900 207 " " " " 10 34.3 5400 208* " " " " 20 33.2 4300 +1.+-.5 209 " " " 3.0 3 33.5 5800 210 " " " 7.0 0.5 33.2 4500 211* " " " 10.0 3 31.1 3900 212 36 38 26 0.5 1 35.5 7800 213* " " " " 20 32.6 5500 214 " " " 1.5 3 34.4 7500 215 " " " " 10 33.3 6800 -7.+-.4 216 " " " 3 3 33.4 6800 217 " " " 7 10 31.1 4500 218* " " " " 20 30.2 3400 219* " " " 10 10 30.0 4000 220 40 48 12 0.5 10 36.8 5300 221 " " " 1.5 3 37.8 6400 222 " " ` 3 1 37.9 5800 +9.+-.4 223* " " " 7 20 33.7 2300 224* " " " 10 3 34.7 3800 __________________________________________________________________________ The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.